This invention relates to a froth coated paper substrate having improved opacity and ink hold-out; more particularly it relates to a process of forming a paper product by applying to the surface of a paper substrate at least one coating of frothed elastomeric resin emulsion containing inorganic solids, compressing the froth coating after partial curing to obtain a thin densified surface layer of the frothed coating emulsion to produce a lightweight coated paper. The invention also relates to a froth coated paper substrate sized with a frothed elastomeric resin emulsion containing starch solids, or starch solids per se, in which the starch solids and/or resin-starch solids remain at or near the surface of the substrate in the form of a sizing.
The prior art has been for a long time reflecting work on improving the coating or surface treating of paper, particularly in the area of improved opacity and ink hold-out. The patents to Reilings U.S. Pat. No. 3,002,844 and U.S. Pat. No. Re. 25,884 show coating of paper by using a pigment paper coating of a mixture of water-soluble gum, alkali-soluble, water-soluble protein, and paper pigments to eliminate cast coating and thus produce a very thin or lightweight coat application to the surface of paper.
In the patent to Rasmussen et al U.S. Pat. No. 3,413,139, improved ink hold-out and a modification of surface characteristics of paper were produced by applying to a continuously moving web of paper a plurality of coats or aqueous mineral pigment and a binder and drying after each coat, followed by calendering the coated paper only prior to the last coating operation. The patent to Graulich et al U.S. Pat. No. 2,999,773 discloses a process for producing sheet material, including paper, by applying to one side of a compiled fiber web a coating of latex foam, passing the coated material through a dryer and, after treating the other side with latex foam, passing the web between nip rolls and through a dryer to produce a sheet material impregnated on both sides. Simulated leather was formed by the processes set forth in the patent to Brodnyan et al U.S. Pat. No. 4,061,822 by coating a nonwoven web with a foam, partially drying it, and then applying a compressive crushing of the partially dried foam followed by plating or embossing to form the substitute leather product after a final heat curing.
As will become apparent, the present invention presents an improved coated paper product, paper coating composition, and method of forming same which provides the paper industry with a thin lightweight coating that exhibits greater opacity and print hold-out with the use of a lesser amount of a coating composition thus permitting the use of thinner paper substrates than heretofore usable in the art.